as those posts [1], [2], [3] are at least one year old and I can not find any information [4] about the current differences between the versions (are there any?) I would like to know whether the current GPL-licensed version of agsXMPP SDK supports GSSAPI or not.

about the current differences between the versions (are there any?) I would like to know

currently the only difference is the GSSAPI SASL mechanism. We were planing more extensions for the commercial version but then started the MatriX SDK which is the successor of asgXMPP with new features.

Quote by sc911:

whether the current GPL-licensed version of agsXMPP SDK supports GSSAPI or not.